Reply To: Voltage divider on multipurpose screw adapter

Hi Matt, sorry I didn’t see your original post from last week.  You are correct in how the resistor divider works, we have several sensors that have a 0-5v DC output, so dividing it in half makes it safe to read with the 3.3v-based circuitry of the Mayfly’s ADS1115.  However, you can also use mismatched resistors to create a divider for something like a 0-12v signal too.

Are you sure you need to use differential measurement of the sensor analog output?  Many analog-out sensors have separate power and signal ground lines, but sometimes the manufacturer says it’s okay to connect the signal and power ground wires to the same point.  If that’s the case, then you can use the screw terminal board as it was designed by changing over one of the solder jumpers (like JP1) and adding matched resistors to R1 and R2.  I haven’t used that particular Turner turbidity sensor, but all of the other Turner sensors I’ve used have allowed me to connect signal ground to power ground.

But if you’re sure you need to use differential measurement, then there’s no easy way to use the screw terminal board since the divider circuitry is based on using the ground pin from the Mayfly as the common wire for the divider.  You could modify your board by either cutting traces or by hacking/splicing the Grove cable between the screw terminal board and the Mayfly and adjust which wires go to where, but using a common ground would be a much simpler approach if that will work with your sensor.